Residential and commercial air conditioners include as a part thereof a fan coil unit. The fan coil unit includes a coil through which coolant (liquid or gas) is pumped, and normally the coil is above a condensation pan or convector tray having one or more openings through which air is blown by one or more fans. The air passing through the coil creates condensation on the coil which drips down upon the convector tray and then is conducted by an appropriate outlet and pipe to a drain.
Such convector trays are generally made from galvanized metal and rust with relative ease. Once a convector tray rusts the water might, for example, drip down and into the underlying motor(s) which drives the fan(s), causing the latter to shortout. Continuing rust also blocks or reduces normal drainage which results in fungus growth which in turn can also cause odors and also cause the normal drain opening to close or appreciably block the same with, of course, attendant overflow and damage.